30-nm InAs PHEMTs With $f_{T} = \hbox{644}\ \hbox{GHz}$ and $f_{\max} = \hbox{681}\ \hbox{GHz}$

Abstract

We present 30-nm InAs pseudomorphic HEMTs (PHEMTs) on an InP substrate with record fT characteristics and well-balanced fT and fmax values. This result was obtained by improving short-channel effects through widening of the side-recess spacing (Lside) to 150 nm, as well as reducing parasitic source and drain resistances. To compensate for an increase in Rs and Rd due to Lside widening, we optimized the ohmic contact process so as to decrease the specific ohmic contact resistance (Rc) to the InGaAs cap to 0.01 Ω·mm. A 30-nm InAs PHEMT with tins = 4 nm exhibits excellent gm,max of 1.9 S/mm, fT of 644 GHz, and fmax of 681 GHz at VDS = 0.5 V simultaneously. To the knowledge of the authors, the obtained fT in this work is the highest ever reported in any FET on any material system. This is also the first demonstration of simultaneous fT and fmax higher than 640 GHz in any transistor technology.